While I was playing my Valveking earlier today, I turned it on and this horrible buzzing sound came from the amp and almost no volume. I'm thinking its a tube, so i look back and my "Big" tubes look fine.. a little blue glowing but not a whole lot. I take the casings off the pre amp tubes and It seems like 1 or 2 of them are blown...

i cant really tell though because im not really experienced in this stuff

can you guys tell me how i can tell if the tubes are messed up or if its some other kind of problem

thanks in advance